fix: error-pages graded healthy, unwired sensors listed apart, Maintenance failed reads 0 (#5780, #5781, #5782)

- #5780 "The error-pages service is graded on other routers' errors". The
  Traefik scrape reads which services an errors middleware sends to, and
  grades them healthy: their 4xx and 5xx are the codes of the errors they
  cover for, already graded on the routers that failed.
- #5781 "The Maintenance failed rules sit at no data until a host has had
  a maintenance job". Every host with an agent reads 0 until a job fails.
- #5782 "VDNT-Util01's host page lists SYSTIN at 115 °C in red". The host
  page lists sensors that counts_as_hottest leaves out (unwired board
  inputs, 0 °C or below) on one muted line, not as heat.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plugins/host_agent/routes.py

@@ -113,6 +113,17 @@ def counts_as_hottest(label: str, celsius: float) -> bool:
     return not (_BOARD_INPUT.match(label) and celsius >= BOARD_INPUT_CEILING_C)
 
 
+def split_temps(temps: dict) -> tuple[dict, dict]:
+    """(real, unwired): a host's sensors, hottest first, apart from the ones
+    counts_as_hottest leaves out (a board input with nothing wired to it, a
+    reading at or below 0 °C). Those read a constant at any load, so the
+    page lists them apart instead of colouring them as the host's heat."""
+    def by_heat(d: dict) -> dict:
+        return dict(sorted(d.items(), key=lambda kv: -(kv[1] if kv[1] is not None else -999)))
+    real = {k: c for k, c in temps.items() if c is None or counts_as_hottest(k, c)}
+    return by_heat(real), by_heat({k: c for k, c in temps.items() if k not in real})
+
+
 def _ts_or(value, fallback: datetime) -> datetime:
     """An agent-sent ISO time, or `fallback` when it isn't one."""
     try:
@@ -856,12 +867,13 @@ async def host_detail_metrics(host_id: str):
             HostAgentRegistration.host_id == host_id))).scalar_one_or_none()
         latest = await _latest_metrics_for_host(session, host.name)
     hostlvl, cores, nets, disks_io, temps, mounts = _split_host_metrics(host.name, latest)
+    temps, unwired = split_temps(temps)
     ls = reg.last_seen_at if reg else None
     stale = ls is None or (datetime.now(timezone.utc) - ls).total_seconds() > _stale_after_seconds()
     return await render_template(
         "_host_metrics.html",
         host=host, reg=reg, stale=stale, hostlvl=hostlvl,
-        cores=cores, nets=nets, disks_io=disks_io, temps=temps, mounts=mounts,
+        cores=cores, nets=nets, disks_io=disks_io, temps=temps, unwired_temps=unwired, mounts=mounts,
     )